As the leaders left, the green-and-white banners were still festooned outside Phnom Penh’s Peace Palace, a fitting reminder of China’s powerful and growing clout as Beijing uses its influence - and money - to win friends and frustrate those uneasy about its sweeping territorial claims and rising military strength.

“Some states are easily swayed by money. If they see cash, they easily throw away their principles,” said one Asian diplomat at the East Asia Summit, which included heads of state from 10 Southeast Asia countries and counterparts from the United States, China, Japan and other Asia-Pacific nations. “China has been throwing its weight around and buying the loyalties of some Asian states.”

A prime example is Cambodia, whose prime minister, Hun Sen, helped China to notch up a succession of diplomatic victories at the summit. China stalled debate on a resolution of maritime disputes in the South China Sea, rebutted attempts by Southeast Asian nations to start formal talks on the issue and avoided any rebuke from Obama over territorial ambitions. Commentators declared China a clear summit winner.

A closing statement by Hun Sen, this year’s chair of the 10-member Association of Southeast Asian Nations (Asean), made no mention of the South China Sea, another victory for China's attempts to prevent multilateral talks on the dispute.

China has poured investments and loans into Cambodia in recent years, becoming its biggest trade partner and bilateral creditor. Cambodia’s debt to China now totals at least $4.7 billion, about a third of its economy. The price of that largesse has become clear this year, say analysts, as Cambodia has used its powers as ASEAN chair to restrict debate over the vexed issue of China’s maritime claims, dividing the group and infuriating US ally the Philippines.

The 45-year-old Asean group has been built on a foundation of unanimity and unity, but that has unravelled as it struggles to cope with its biggest security challenge. In July, a meeting of the region’s foreign ministers broke down and failed to agree a communique for the first time.

This week’s Asean meetings again deteriorated into bad-tempered sniping and came close to a breakdown when Hun Sen adopted a draft statement saying there was a consensus not to “internationalise” the South China Sea dispute beyond Asean and China.

The Philippines, which sees its alliance with the United States as a crucial check on China’s claims at a time when Washington is shifting its military focus back to Asia, made a formal protest to Cambodia and succeeded in having that clause removed from the final statement.